Alan Gets Blog Cred ~ Rethinking The Roof on Container Three

In this post I talk about the roof over container three. I planned to pour a concrete slab.

In my previous post, Wallito, reader Alan wrote an extensive comment* (repeated below in its entirety) about the roof on container three. Thank you for going out on the limb to suggest an alternative solution. Most guys won’t give another guy suggestions or advice unless we ask for it. We don’t want to cut in on another guy’s turf. But thanks Alan, you did, and you did it with grace and class.You made me think, especially when you mentioned the half-life of caulking.

And another thing happened. We have had some wicked heavy rain since I applied the urethane caulk yesterday and the caulk all washed away. I thought it was urethane, but it turns out that it is urethane enhanced elastomeric caulk in a latex base. The urethane caulk that I have been using elsewhere on the containers is sticky-gooey in a non-latex base. It cures fast and remains flexible. Water doesn’t affect it even if it isn’t cured, but this elastomeric caulk didn’t have enough time to develop a water-resistant skin. Bye bye three tubes of caulk.

In my construction career I learned not to trust caulk of any kind for any mission-critical project. Make joints tight and right. But I guess I forgot or got lazy. Reminds me of the painter’s saying, “A little putty, a little paint, makes a carpenter what he aint.” Thanks Alan for bringing this to my attention.

Alan also mentioned that the concrete slab would accumulate heat during the day. Very true, and I was going to put a sheet of foam insulation under the concrete.

I was going to use the concrete slab on the roof of container three to direct water off the roof. This roof will handle a lot of water. If we look at the photo of the model again, you can see that two significant roofs dump onto number three.

The model is somewhat lacking, as there is actually a two-foot high wall on the right side of container three, and that wall is the tilebacker wall that I just detailed in Wallito:

I am going to duplicate this wall on the left side of the container for the other roof to sit on.

The concrete slab is now off the table. Alan suggested installing a sloped roof using cement board roofing tiles. Alan, I’m going to take your sloped roof idea, thank you, but I think I’ll use the corrugated metal roofing sheets that I am using on the other roofs. Several of our friends have the cement board roofing panels and they seem to need more maintenance to keep the green slime pressure washed off the roof. Also, it is slicker than slick to walk on and I see a lot of broken tiles. The metal roofing is not elegant in any way, but it is economical and the only potential leak points are where the screws penetrate the metal making it easy to diagnose and maintain. Another advantage of the metal roofing is that it is highly reflective and doesn’t accumulate a lot of heat.

With the two-foot high walls, I can easily construct a roof over number three that slopes from about eighteen inches at the high end down to nothing at the other end of the container.

The metal roofing is flexible and I can roll it up the wall and screw it in place. The screws won’t hold in the tilebacker, but I can place a carriola behind the tilebacker to receive the screws. Armando and I can work together; he on one side of the wall and me on the other.

I can also use Alan’s idea of the roll insulation placed directly on the container roof below the new sloped roof.

In other happenings, today was a near washout with torrential rains beginning at 10:30 a.m. But I did manage to spray two coats of white paint on the exterior of the 12-foot wall between three and four, and between raindrops I got one piece of tilebacker up on the triangular wall section.

That’s all for now. Thanks again Alan.

*Here’s Alan’s comment in its entirety:

Hi Fred,

Thanks for your most recent update. I’m enjoying the process of your build and I am taking notes for that day when I will also build a container home or container something.

In any case, I wanted to chime in regarding your roof and give you an unsolicted opinion. You know what that’s worth!

You may have already thought through your process so please don’t look upon my advice as expert, other than I’m building my own home and have lots of experience with leaky buildings especially where I come from (Pacific Northwest). I am also building a home in Panama and it’s a learning experience for me also.

With regards to mixing different elements like concrete, caulking, and metal; these are all materials that expand and contract differently. So it’s almost guaranteed that eventually your caulking will separate from your metal. If you put concrete over the seal, it may help but the mass of the concrete will expand at different rate as the metal on the roof. If the concrete cracks due to this dynamic, it’s possible water could penetrate the concrete and this will require you to seal and paint the concrete regularly to keep it from taking on water.

So, my thought is to suggest a slightly sloped roof for the top of our container made from concrete board (plysem) that is corregated and also conveniently stained red. The plysem overlap each other in the installation so you have a sealed, overlaping joint wherever they meet. The corrugated look may not be what you are looking for so this is also a consideration. I have installed on my own roof and it looks good the way it is despite the fact that I am installing reclaimed clay roof tiles on top of the plysem.

With regards to where the plysem meets your newly installed concrete board wall, you would simply install an L shaped flashing that covers the top of the plysem where it meets the wall by at least 5 inches and goes up your concrete board wall by the same amount. You can later cover your concrete board with a repelo to hide the flashing that’s attached to the concrete board wall. Ideally, the flashing would have been placed behind your concrete board and extended outward to cover the plysem but you’ve already got your board up and this will work just as well.

This should also allow you to install a radiant barrier (plastised aluminum sheet ) underneath your plysem directly on the top of your container roof. This is a cheap way to reduce your cooling and reduce the temperatures of your house. You can pick radiant barrier at Hopsa for about $96 per roll 4′x100″.

The other thing you need to be aware of is if you choose to use concrete to cover the top of the container, it wll also collect heat all day and dissipate into your interior as it will be directly connected to the metal on your roof that I believe is also the ceiling in your rooms.

You can overlap and tape the radiant barrier by a few inches and it also acts as an emergency secondary barrier for any leaks that may come through your plysem roof. The radiant barrier will most definitely reduce the amount of heat entering your home as it acts to deflect infra-red heat back up and into the plysem. You need to make sure there is at least one to two inches separating the radiant barrier and the plysem and the corrugated part of this concrete board provides sufficient space between the two.

Again, only a thought and most likely not what you’ve spec’d but may be worth the consideration.

1 thought on “Alan Gets Blog Cred ~ Rethinking The Roof on Container Three

  1. Thanks Fred,

    That’s a nice compliment.

    I figured you would be the kind of guy that might appreciate someone elses opinion and not take offense. I’m a lot like that too.

    In any case, I think the metal roof is a great choice now that you can bend the sides up your concrete wall and saves the hassle of installing a flashing. The radiant barrier is the best investment you can make in any hot temperate climate. $96 for a 4’x100′ roll will pay for itself in a year if you plan on using air conditioning.


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